Marker structure, mask pattern, alignment method, and lithographic method and apparatus

Abstract

A mask pattern for imaging a marker structure on a substrate with a lithographic apparatus, the marker structure being configured to determine optical alignment or overlay, includes constituent parts to define the marker structure. The constituent parts include a plurality of segments, each segment having substantially a size of a device feature and a segment shape. The mask pattern includes at least one assist feature located at a critical part of the segment shape. The at least one assist feature has substantially a size below a resolution of the lithographic projection and is configured to counteract optical aberrations or optical limitations generated in the lithographic projection at the critical part.

1 . A mask pattern for imaging a marker structure on a substrate with a lithographic apparatus, the marker structure being configured to indicate a position, the mask pattern comprising a plurality of constituent parts to define the marker structure,
 wherein each of the constituent parts includes a plurality of segments arranged in a direction substantially perpendicular to a scanning direction of the lithographic projection, and   wherein the segments of the constituent parts have substantially the same shape, and   wherein each segment has substantially the same size as a device feature to be imaged onto the substrate.   
   
   
       2 . A mask pattern according to  claim 1 , said pattern comprising at least one assist feature having a size less than a resolution of the lithographic apparatus, and
 wherein each of said at least one assist feature is located at a corresponding critical part of the segment shape.   
   
   
       3 . A mask pattern according to  claim 2 , wherein said at least one assist feature includes a block-shaped segment located near a corner of a rectangular segment. 
   
   
       4 . A mask pattern according to  claim 2 , wherein the at least one assist feature includes a line-shaped segment located near an outer edge of a plurality of line-shaped segments. 
   
   
       5 . A mask pattern according to  claim 2 , wherein said assist feature is configured to counteract an optical effect of the lithographic apparatus at the critical part. 
   
   
       6 . A marker structure generated by a mask pattern in accordance with  claim 1 . 
   
   
       7 . A mask pattern for imaging a marker structure on a substrate with a lithographic apparatus, the marker structure being configured to indicate a position, the mask pattern comprising:
 a plurality of constituent parts to define the marker structure; and   at least one assist feature having a size less than a resolution of the lithographic apparatus,   wherein each of the constituent parts includes a plurality of segments having substantially the same shape, and   wherein each segment has substantially the same size as a device feature to be imaged onto the substrate, and   wherein each of said at least one assist feature is located at a critical part of the segment shape.   
   
   
       8 . A mask pattern according to  claim 7 , wherein said at least one assist feature is configured to counteract an optical effect generated by the lithographic apparatus at the critical part. 
   
   
       9 . A mask pattern according to  claim 7 , wherein said at least one assist feature includes a block-shaped segment located near a corner of a rectangular segment. 
   
   
       10 . A mask pattern according to  claim 7 , wherein the at least one assist feature includes a line-shaped segment located near an outer edge of a plurality of line-shaped segments. 
   
   
       11 . A mask pattern for imaging a marker structure on a substrate with a lithographic apparatus, the marker structure being configured to indicate a position, the mask pattern comprising:
 a plurality of constituent parts to define the marker structure, and   a plurality of isolated elements,   wherein each of the constituent parts includes a plurality of segments having substantially the same shape, and   wherein each segment has substantially the same size as a device feature to be imaged onto the substrate, and   wherein the plurality of isolated elements is configured such that a beam of radiation patterned by said mask pattern substantially fills an aperture of a projection system of said lithographic apparatus.   
   
   
       12 . The mask pattern according to  claim 11 , wherein said marker structure is configured for use in determining an overlay relationship between successively imaged patterns. 
   
   
       13 . The mask pattern according to  claim 11 , wherein a dimension of each of the plurality of isolated elements is less than a resolution of the lithographic apparatus. 
   
   
       14 . The mask pattern according to  claim 11 , wherein a pitch of the plurality of segments of at least one of the constituent parts is substantially equal to a pitch of a pattern of device features to be imaged onto the substrate. 
   
   
       15 . A lithographic projection apparatus comprising:
 a radiation system configured to provide a beam of radiation;   a support structure configured to support a patterning structure, the patterning structure configured to pattern the beam of radiation;   a substrate table configured to hold a substrate having at least one marker structure configured to indicate a position;   a position detection system configured to optically determine a position of the marker structure; and   a projection system configured to project the patterned beam onto a target portion of the substrate;   wherein the at least one marker structure comprises a plurality of constituent parts, each constituent part including a plurality of segments arranged in a direction substantially perpendicular to a scanning direction of the lithographic projection, and   wherein the segments of the constituent parts have substantially the same shape, and   wherein each segment has substantially the same size as a device feature to be imaged onto the substrate.   
   
   
       16 . The lithographic projection apparatus according to  claim 15 , wherein said position detection system includes at least one of the group consisting of an alignment system and an overlay system. 
   
   
       17 . A method of imaging a marker structure on a substrate with a lithographic apparatus, the marker structure being configured to indicate a position, the method comprising:
 patterning a beam of radiation with a mask pattern; and   projecting the patterned beam of radiation onto a target portion of the substrate,   wherein the mask pattern comprises a plurality of constituent parts to define the marker structure,   wherein each of the constituent parts includes a plurality of segments arranged in a direction substantially perpendicular to a scanning direction of the lithographic projection, and   wherein the segments of the constituent parts have substantially the same shape, and   wherein each segment has substantially the same size as a device feature to be imaged onto the substrate.   
   
   
       18 . The method of imaging a marker structure according to  claim 17 , said pattern comprising at least one assist feature having a size less than a resolution of the lithographic apparatus, and
 wherein each of said at least one assist feature is located at a corresponding critical part of the segment shape.   
   
   
       19 . The method of imaging a marker structure according to  claim 17 , wherein said at least one assist feature includes a block-shaped segment located near a corner of a rectangular segment. 
   
   
       20 . The method of imaging a marker structure according to  claim 19 , wherein the at least one assist feature includes a line-shaped segment located near an outer edge of a plurality of line-shaped segments. 
   
   
       21 . The method of imaging a marker structure according to  claim 19 , wherein said assist feature is configured to counteract an optical effect of the lithographic apparatus at the critical part.